Re: Fun-O Basic Edition Compiler

[Bruce Hoult <address@hidden>]

In article <3C3234FC.7060508@quiotix.com>, Jeffrey Siegal 
<jbs@quiotix.com> wrote:

> Bruce Hoult wrote:
> 
> > In article <3C321156.1020709@quiotix.com>, Jeffrey Siegal 
> > <jbs@quiotix.com> wrote:
> > 
> > 
> >>>You can always declare a particular value to have a more restricted 
> >>>type.
> >>>
> >>Is there such a type in Dylan?
> >>
> > 
> > Millions of 'em...
> > 
> >   limited(<integer>, from: 20, to: 4123)
> 
> Not exactly.  What I was getting at would use the "natural" limits of a 
> machine integer (like the native <integer> but with overflow checking). 
> Is there a way of specifying that?

I don't know what FunctionalDeveloper does.  We don't have such a type 
in Gwydion Dylan.

More than that, I don't know how to efficiently implement one in 
portable ANSI C, otherwise I'd be happy to add one.  Which would also 
allow us to make our bignum support a lot more efficient (it currently 
works on 16 bit "digits").

Detecting addition overflow of unsigned numbers is easy and efficient: 
if (a+b) < a then you have overflow.  For signed 2s-complement it's a 
little more work, but OK, such as: "r=a+b; if ((r^a)^(r^b) < 0) 
overflow()".

How can you do it for multiplication, other than by dividing afterwards 
and comparing, or pre-classifying the operands?


OTOH, maybe it's time for Gwydion to have just a *little* assembler.  
That's not nice given that it runs on a number of different CPUs, but 
maybe it's not *too* bad: x86 and PPC will cover most people.  SPARC and 
MIPS and HPPA and IA64 would probably get the rest.

-- Bruce